The behaviour of ferritic weldments in thick section 12Cr12Mo14V pipe at elevated temperature

Abstract A major collaborative research programme is being carried out within the CEGB to examine the correlation between data, produced from a range of test methods, which are currently used in the design of welded steam pipes. In the part of the programme reported here, the elastic and creep deformation occurring in low alloy ferritic steel pipe-to-pipe weldments has been studied in pressure vessel experiments conducted at 565°C and 455 bar internal steam pressure. The welds were made in 1 2 Cr 1 2 Mo 1 4 V parent pipe using mild steel and low alloy 1CrMo, 2CrMo and 1 2 CrMoV weld metals. All the weldments were post-weld heat treated for 3 h at 700°C prior to testing. In addition, the weldments, represented as parent material, heat affected zone and weld metal, have been analysed to determine stresses and strains using a finite element three-material model. The main features of the macro- and micro-structures of the four weldments are briefly described. Results are then presented for the elastic and creep deformations observed in both the hoop and axial directions in the weldments. The experimental creep strain data are then used as a basis for calculating the stationary state stresses present on the surface of the weldments. The surface stationary state stress distribution and corresponding steady state strain rates, determined using the finite element model, are then presented. The pressure vessel experimental results and the data from the finite element analysis are discussed in terms of the hoop and axial deformation in the weldments. An assessment is then made of the correlation between the results from the experimental and analytical approaches. Finally, the practical implications of the present results are considered with respect to the design of operating plant.